Dye bleaching process



Patented Aug. 3, 1943 DYE BLEACHING PROCESS Robert A. Morris, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey,

No Drawing. Application June 6, 1942, Serial No.

446,054. In Great Britain August 19, 1941 4 Claims.

This invention relates to color photography and particularly to a bleaching method of forming dye images.

It is well known that in the dye bleaching method of color photography in which a dye uniformly dispersed in a photographic emulsion layer is bleached in the region of a'silver image, a positive image is produced when the layer is exposed to'a positive scene or image. According to the usual procedure a silver halide layer containing the dye from which the image is produced is exposed to a positive and developed to a negative silver image. The layer is then fixed and the dye bleached in the region of the negative silver. This leaves a positive dye image.

It is frequently desirable to produce a negative print or transparency by the dye bleaching method when printing from a color positive or a positive color print or transparency when printing from a color negative. To produce such print or transparency of color aspect opposite to the original, by the usual dye bleaching method, it is necessary to resort to a reversal process. According to this process the negative silver pro duced upon first development mustbe first removed and this step alone is frequently difficult since the image forming dye must not be destroyed in the operation. It is thennecessary to convert the residual silver halide to metallic silver to form the agent which determines the bleaching of the dye. This procedure requires a great number of stepssand introduces difficulties in the choice of baths suitable for removal of the silver.

It is therefore an object of the present invention to provide a dye bleaching process of color photography in which a negative color image is produced from a positive original or a positive color'image is produced from a negative color original. A further object is to provide a method for the production, of a natural color positive imageby the dye bleach method.

These objects are accomplished by exposing a silver halide layer containing a uniform dispersion of an image-forming dye, developing it, removing the metallic silver and bleaching the dye in the regions of the residual silver halide. This method avoids the separate step of converting the residual silver halide to metallic silver to form the agent which determines the regions in which the dye is bleached.

My process is applicable to multi-layer films as well as single layer films and is particularly from color negatives consisting of dye images. For example, a film exposed to a color negative or successively to color separation negatives bleaching operation in order to produce a. clear through suitable filters is processed by the following steps.

One of the features essential to the operation of my process is a method for bleaching the dye in the presence of silver halide rather than metallic silver. A method for accomplishing this bleaching of the dye is described in the copending application of Ehrenfried, Serial No. 360,622,

filed October 10, 1940. According to the method described in that application, certain azo dyes may be bleached in the region of a silver halide image by treatment in sodium stannite. During the bleaching operation the silver halide is converted to metallic silver and the silver formed in this way must be removed at the end of the and transparent dye image. Thisremoval of the silver, however, adds no additional steps to the normal process, since silver bleaching and fixing steps are necessary even in the case of bleaching in the presence of metallic silver.

The following example illustrates a multi-layer film which is suitable for processing according to my invention.

on a support of cellulose ester, glass, paper, synthetic resin or other suitable material, there are coated gelatino silver halide layers sensitive respectively to the red, green and blue regions of I movable dye or a layer of colloidal silver.

suitable for making prints from motion picture color separation negativeswith silver images or acetanilideand coupling it in acid solution with The red-sensitive layer has incorporated there-' in a cyan dye made by diazotizing p aminoethoxy Cleves beta acid (1-naphthylamine-2- ethoxy-6-sulfonic acid), again diazotizing and coupling in alkaline solution with p-aminobenzoyl gamma acid 2(p-aminobenzoylamino) 8- naphthol-G-sulfonic acid. This dye has the following structural formula:

The green-sensitive layer is colored with the dye formed by diazotizing 4,4'-diamino-3,3',6,6'- tetramethyltriphenylmethane andcoupling it in alkaline solution with two moles of heptoyl H acid (1 heptoyl amino 8 naphthol 3,6-disulionic acid). This dye has the following structure:

a N8 8 O S O|Na NaS O OaNa The unsensitized layer is colored with the dye made by tetrazotizing 4,4 diaminostilbene-2,2'- disulfonic acid and coupling it in alkaline solution with two moles of phenol and forming the di-npropy1 ether of the product. This dye has the following structure:

CHa(CH2)2-OON= Gabon An alternative dye for the unsersitized'layer is the following:

The dye formed by diazotizing 2(p-aminobenzoylamino) naphthalene-6,8-disulfonic acid, coupling it in acid solution with m-phenetidine, and treating the resulting product with phosgene to form the urea dye. This dye has the following structure:

som 0 ocim H II NC N=N NH NaSO 1 l =0 scam 0cm,

An alternative dye for the red sensitive layer is the following:

The cyan dye formed by diazotizing metanilic acid, coupling it in acid solution with l-naphthylamine-'l-sulfonic acid, diazotizing and coupling in acid solution with ethoxy Cleves (1,6) acid (1 napthylamine 2 ethoxy fi-sulfonic acid) and coupling in alkaline solution with the product of v the reaction of diazotized metanllic acid coupled in acid solution with J acid (2,.-amino-5-naphthol-7-suli'onic acid).

5 The following processing procedure is suitable for the multi-layer element described above.

0 H II N-C NH:

After exposure, the element is developed in the The element is then treated in a stop bath containing 33 cc. per liter glacial acetic acid, washed and thesilver is removed in the following bath:

Potassium bichromate grams 2.5 Sulfuric acid.- cc 5 Water toliter" 1 The element is then treated in 200 grams per 35 liter sodium bisulfite solution and washed. The

dye is then bleached in the region of the residual silver halide by treatment for about five minutes in the following bath:

4b Stannous chloride grams 40 Sodium hydroxide do 46 .Triethanolamine cc 50 Water to liter 1 some The silver is then bleached to silver halide in the following bath:

Cupric chloride grams 100 Hydrochloric acid cc 25 Water to liter 1 This is followed immediately by the following silver halide removal bath:

Hypograms 240 Sodium sulflte (desiccated) do 1 15 Acetic acid (28%): cc 48 Sodium metaborate grams 15 Potassium alum do 15 Water to liter 1 5 With certain image-forming dyes it is sometimes advantageous to treat the element in a clearing bath before and after the dye bleach. A clearing bath of the following composition used for five minutes before bleaching in order to re---- move calcium salts which affected bleaching of certain dyes is suitable:

Sodium benzoate grams 1.2 Sodium citrate do 30 Citric acid do 20 Water to.. liter 1 Sodium citrate grams 30 Sodium sulflte do.... 30 Citric aciddo 20 Water to liter 1 My invention is susceptible of the modifications falling within the scope of the appended claims.

I claim:

1. The method of producing a reversed dy image in a photographic silver halide layer containing a uniform dispersion of an azo dye, which comprises exposing said-layer, developing a silver image therein, removing said silver image without afiecting .the residual silver halide, and then bleaching the dye in the region of the residual silver halide in a bleach bath comprising a stannite of an alkali metal. I

2. The method of producing a positive dye image in a photographic silver halide layer containing a uniform dispersion of an azo dye, which comprises exposing said layer to a negative image, developing a silver image therein, removing said silver image without affecting the residual silver halide, and then bleaching the dye in the region of the residual silver halide in a bleach bath comprising a stannite of an alkali metal.

3. The method of producing a positive dye image in a photographic silver halide layer containing a uniform dispersion of an azo dye, which comprises exposing said layer to a negative image, developing a silver image therein, removing saidsilver image in an acid bichromate bath without affecting the residual silver halide, and then bleaching the dye in the region of the residual silver halide in a bleach bath comprising a stanm'te of an alkali metal.

4. The method of forming a natural-color photographic image in a multi-layer element having at least one gelatino-silver halide layer containing a uniform dispersion of an azo dye, which comprises exposing said element to a color negative, developing a silver image therein, removing said silver images without afiecting the residual silver halide, and then bleaching the dye in the regions of the residual silver halide in a bleach bath comprising a stannite of an alkali metal.

ROBERT A. MORRIS. 

